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Wednesday, June 15, 2011

Maniraptor Feathers Part III: The Asian Maniraptors are Not Aberrant

I've seen it casually suggested on occasion that as, to date, direct evidence of feathers has mostly been found in Asian coelurosaurs, coelurosaurs found elsewhere wouldn't have had feathers.

Which is complete crap, of course.

There is no evidence that Asia was somehow different in some way from other parts of the world that would cause maniraptors to have feathers. There's also no evidence that any maniraptor outside of Asia did not have feathers, even though phylogenetic inference predicts that the default assumption should be that all maniraptors have feathers.

Besides, even among only the maniraptors that are known to preserve direct evidence of feathers, they still represent taxa from multiple different formations (some with vastly different paleoenvironments), multiple maniraptor lineages with greatly varying lifestyles, and a time span of 95 million years. There's no indication that these taxa shared anything specific with each other that aren't shared with other maniraptors. And there's also the fact that fossil dinosaurs which preserve evidence of feathers are known from outside of Asia, such as Rahonavis and Juravenator. (And Archaeopteryx, but no one cares because it's a de facto "bird". We again see the recurring theme of differing treatment between de facto "birds" and other types of maniraptors, even though there is no logical basis behind such behavior.)

The fact that extensive scales are known from other dinosaurs outside of Asia means nothing, because these skin impressions represent those from abelisaurids, titanosaurs, carnosaurs, ceratopsians, thyreophorans, and ornithopods, not maniraptors. It's not as though extensive scaly impressions aren't known from Asian dinosaurs: at least one Psittacosaurus specimen from the Yixian preserves scaly skin over most of its body (albeit along with enigmatic bristles on its tail). Tellingly, it's a ceratopsian instead of a maniraptor, showing that phylogenetics is indeed more important in determining integument than arbitrary political and geographic divisions... as it should be. The only reason the Yixian, Jiufotang, and Tiaojishan maniraptors preserve integument is because they were "lucky" enough to die in an environment conductive to soft tissues. Nothing more. Other Mesozoic dinosaurs must rely on the occasional skin impression or badly preserved integument (as in Shuvuuia), or subtle skeletal features such as quill knobs (which may not be immediately obvious; it took more than eighty years for them to be identified in Velociraptor, after all) if direct evidence of their integument is to be obtained. As far as we can tell, the presence of integument on a given taxon has nothing to do with location.

The notion that only Asian non-avian maniraptors had feathers has so many giant holes in it one could fly a Pelagornis through it. It is evidently just another example of desperate wishful thinking, although clearly not much "thinking" has been put into it.

3 comments:

"The fact that extensive scales are known from other dinosaurs outside of Asia means nothing, because these skin impressions represent those from abelisaurids, titanosaurs, carnosaurs, ceratopsians, thyreophorans, and ornithopods,"

I didn't mention those because they're more just skin patches instead of scales over a large part of the body (as known in Carnotaurus, hadrosaur "mummies", Triceratops, titanosaur embryos, Concavenator, etc.).